It is known that a major impediment in achieving high luminous efficiency in incandescent lamps is that many of the systems for converting energy into visible light result in the production of significant quantities of long wave-length infra-red emission to which the eye does not respond. Such emission occurs at the expense of visible light of short-wave length.
In the past, the temperature of a radiating body has been elevated or radiating species have been contemplated which limit the emissions of the radiating body in the infra-red region. Raising the temperature results in a shifting of the black body radiation curve that sets the upper limit of emissions towards shorter wave lengths and permits radiating transitions producing enhancement of visible light. Although advantage of this lift with increasing temperatures is taken to the fullest of which the most favorable materials are capable, it is still well known that incandescent filaments radiate over 90% of their emissions in the infra-red region not perceived by the eye.
Accordingly, the primary object of the present invention is the fabrication of electromagnetic radiators in the shape of a ribbon in which there is emission suppression in the form of an array of cavities in the radiator, the dimensions of the cavities being such that radiation emitted at wavelengths greater than a predetermined wavelength value cannot be propagated by the radiator. The radiator of the present invention suppresses at least a majority of the non-visible infra-red radiation that would otherwise be emitted from it. To provide such suppression, the radiator of the invention has cavities of predetermined widths and regular shapes. The cavities have mean widths of about 350 nm. and are separated by walls of thicknesses less than about one half the mean widths of the cavities, the depths of the cavities being significantly greater than the widths of the apertures so as to suppress emissions of electromagnetic radiation of wave lengths longer than about 0.7 microns without affecting the emission of shorter wave lengths whereby the ratio of emission of infra-red light to that of visible light from the radiators will be substantially reduced thus to increase the luminous efficiency of devices in which they are used. In summary, the cavities have predetermined widths such that only radiation emitted at wavelengths less than a predetermined value can be propagated by the radiator, the predetermined wavelength being selected to suppress a majority of the non-visible infrared that would otherwise be emitted by the device in which it is disposed.